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High‐purity germanium (HPGe) single crystals find their applications as radiation detectors especially for spectroscopy of high‐energy photons and particles in nuclear physics. Growing "detector‐grade" HPGe single crystals, with tailored structural defects and controlled impurity content, uniform throughout the crystal is a challenging task in this type of crystalline semiconductor material. All different process steps for HPGe, namely, i) reducing germanium dioxide powder into Ge metal; ii) zone refining of intrinsic source material (6 N) up to an ultrahigh purity (13 N); iii) Czochralski growth of high‐purity single crystals, are developed in house. A specific preparatory coating process for zone refining is entrenched as part of this work. Gallium, a dominant impurity usually found in HPGe, can be avoided. Using these advanced process know‐hows, a technology to grow volume Ge single crystals of large diameter (3 in.) with very high purity (net carrier concentration ≈ 5 × 1010 cm−3 or equivalent to 1 part per trillion level) is successfully developed. The zone‐refined Ge bars and the crystals show p‐type conductivity. Some crystals exhibit n‐type conductivity, and n–p or p–n transition is encountered in a single growth experiment. Besides the first results of encompassing very high‐purity crystals with uniform diameter, a controlled dislocation density (≈104 cm−2) can be realized. [ABSTRACT FROM AUTHOR]

β-Ga 2 O 3 is an emerging ultra-wide bandgap (4.9 eV) oxide semiconductor that additionally scintillates under gamma excitation. A unique combination of transparency in the UV/visible spectrum, semiconducting, and scintillation properties makes that compound interesting for fundamental studies of underlying physics and design of novel devices, in particular compact detectors for gamma radiation. Undoped, and singly (Ce, Si, Al), doubly (Ce + Si, Ce + Al), and triply (Ce + Al + Si) doped bulk β-Ga 2 O 3 single crystals were grown by the Czochralski method under very similar conditions and systematically studied in terms of electrical and optical properties that were correlated with scintillation light yield under gamma excitation. A wide spectrum of doping enabled to control the free electron concentration in semiconducting β-Ga 2 O 3 crystals within almost three orders of magnitude (7 × 1015–6 × 1018 cm−3) with the Hall mobility approaching 150 cm2 V−1s−1. The maximum of light yield under gamma excitation was recorded for undoped and Ce-doped β-Ga 2 O 3 single crystals having the free electron concentration of mid 1016 cm−3. The light yield significantly decreases for both electrically insulating and highly conducting (Si-doped) crystals. None of the dopants (Ce, Si, Al) introduces any absorption bands in the spectral region of light emission (340–410 nm) under gamma excitation. The dopants in quest do not affect the structure of neither cathodoluminescence (CL) nor radioluminescence (RL) emissions, but modify their absolute intensity. A double-band structure of RL spectra corresponds to UV and blue emissions observed in CL spectra that are assigned to self-trapped excitons. Image 1 • Doped semiconducting β-Ga 2 O 3 was grown and studied for gamma radiation detection. • The crystals are fully transparent to scintillation emissions at 340–410 nm. • Maximum of light yield was found at free electron concentration of mid 1016 cm−3. • Luminescence spectra point to self-trapped excitons in scintillation mechanism. [ABSTRACT FROM AUTHOR]

• Bulk β-Ga 2 O 3 single crystals are grown the Czochralski method. • The crystals are doped with a number of mono-, di-, tri-, and tetravalent ions. • Incorporation of the dopants into bulk crystals is investigated. • Impact of dopants on growth stability and physical properties of crystals is studied. The present report relates to a systematic study of dopant incorporation into bulk β-Ga 2 O 3 single crystals grown by the Czochralski method, and their impact on growth stability, crystal appearance (growth habit), electrical properties, and transmittance of the obtained crystals. At very similar growth conditions, the dopant incorporation is driven mainly by ionic radii difference between dopant and Ga3+ ion and by thermal stability of the dopant during crystal growth. Good growth stability was achieved with Li1+, Mg2+, Co2+, Ni2+, Ce3+, Al3+, and Ge4+ doping, as that resulted in lowering or entirely compensating the free electron concentration (n e), and, in some cases, presence of additional oxygen through a dopant oxide/carbonate decomposition that is added to the starting material. Undoped crystals had the n e of 2.5 × 1016–2 × 1018 cm−3 with the Hall mobility of 80–152 cm2 V−1 s−1. The n e within that range was also achieved by doping the melt with Li1+, Cu1+, Cr3+, Ce3+, and Ge4+. The two former (Li, Cu) and the latter (Ge) dopants entirely evaporate during or even before growth due to very high partial pressures, but at the same time they leave in the melt extra oxygen that affect to some extent (depending on its initial concentration) the n e. Therefore, we provide a new tool to control the free electron concentration at low levels (n e = 1016–1017 cm−3) by doping a Ga 2 O 3 starting material with thermally unstable oxides or carbonates (such as GeO 2 or Li 2 CO 3) that undergo thermal decomposition at high temperatures with entirely evaporated cations and released in the melt an extra oxygen (dopant acting as an additional oxygen source). Si4+ and Sn4+ increase the n e to 2.5 × 1018–1019 cm−3, consistent with previous studies. At such high n e , the Hall mobility drops to values of 50–84 cm2 V−1 s−1. Divalent ions (Mg2+, Co2+, Ni2+) and trivalent Al3+ made the crystals electrically insulating. We also empirically showed that the underlying conductivity of undoped β-Ga 2 O 3 crystals is caused by residual solid impurities, mainly by Si4+ and hydrogen, the latter could be easily removed by annealing. The transmittance near the absorption edge is not affected by the dopants at studied concentrations, except Cr3+, Co2+, and Ni2+ that introduce an extra absorption in the UV and blue spectral regions, and Al3+ that slightly shifts the absorption edge towards shorter wavelengths. [ABSTRACT FROM AUTHOR]